This invention is directed to a method for preparing perfluoroalkyl substituted aromatic compounds. More particularly, the invention is directed to a method for preparing such compounds by reacting a perfluoroalkyl bromide with an aromatic compound in the presence of a catalytic amount of iodine or an iodine generating compound such as trifluoromethyl iodide.
Perfluoroalkyl aromatic compounds are commercially prepared by reacting a perfluoroalkyl iodide with the aromatic compound. British Patent 840,725 describes such a process wherein one mole of the aromatic compound is heated with two moles of the perfluoroalkyl iodide. This process is wasteful of one mole of the iodide in that two moles of perfluoroalkyl iodide are employed to produce each mole of product.
U.S. Pat. No. 2,957,031 describes a process for reacting perfluoro acid halides with aromatic compounds in the presence of nickel carbonyl. The highly toxic nature of nickel carbonyl makes the process commercially unacceptable.
Huyser, Earl S. and Bedard, Ernest, J. Org. Chem 29, 1588 (1964) indicates that the mechanism by which perfluoroalkylation occurs with the aromatic ring involves the formation of a perhaloalkyl free radical which then attacks the aromatic ring. In recognition of this mechanism, U.S. Pat. No. 3,271,441 discloses a process in which the ratio of perfluoroalkyl iodide to aromatic compound is reduced to about 1 by conducting the reaction in the presence of a free radical generating compound selected from the group consisting of organic peroxides and aliphatic azo compounds.
While perhaloalkyl iodides have been used commercially to prepare perfluoroalkyl aromatics, efforts to utilize perfluoroalkyl bromides have been unsuccessful. As shown in copending U.S. patent application Ser. No. 424,394, now U.S. Pat. No. 3,890,326, the uncatalyzed vapor phase reaction of an aromatic compound and trifluoromethyl bromide produces bromine substitution, thus, producing fluoroform and brominated aromatic products to the virtual exclusion of perhaloalkyl substituted aromatics.